A sensing amplifier is often used to read Static Random Access Memory (SRAM) in computing devices. The outputs of the electronic circuits used in SRAMs are relatively weak, and therefore, are slow data line drivers. To provide greater data line driving capability and shorten state transition times of data lines, a sensing amplifier, whose operation is commonly known in the industry, is used to pre-charge the data lines to a known voltage, typically a supply voltage VDD which is 3.0 volts in modern circuits. Once the data lines are released from a pre-charged state, the SRAM data lines transition to the state currently stored in the particular SRAM memory location. The sensing amplifier senses the difference between a data line and its compliment data line as they transition to opposite states. Detection of the difference, by the sensing amplifier, is used to shorten the time required for the data lines to reach their final state.
As computing devices are increasingly powered by batteries, designers of such computing devices seek out technologies which are more energy efficient. In the case of sensing amplifiers, and semiconductors in general, "low leakage" semiconductors are often used. These semiconductors have a greater ability to hold a charge, and therefore, take a greater amount of time to passively discharge or "leak" a charge on a data line or a node into a substrate of the semiconductor. While the low leakage characteristic of the semiconductor reduces its power consumption, it creates an undesirable condition in the sensing amplifier when a sharp increase in the supply voltage VDD occurs.
A sharp increase in supply voltage VDD is conducted to inputs of a latching portion of the sensing amplifier. As the supply voltage VDD returns to nominal VDD voltage in a "leaky" semiconductor, the charge on the inputs of the latching portion of the sensing amplifier quickly leaks into the substrate and normal operation occurs. In low leakage semiconductors, however, the charge remains on the inputs for a longer period of time. The remaining charge sometimes causes a transistor, which connects the inputs of the latching portion to supply voltage VDD, to "turn-off" thereby isolating the inputs from the supply voltage VDD resulting in an undetermined voltage on the inputs to the latching portion of the sensing amplifier. The undetermined voltage on the inputs causes the sensing amplifier to operate in an unreliable manner.
It would be advantageous, therefore, to devise a method and apparatus for pre-biasing inputs to a latching portion of a sensing amplifier to a reliably known voltage. It would be further advantageous if such a method and apparatus performed reliably on "low leakage" semiconductors in the presence of a potentially varying supply voltage.